image industrial radiography

What is the structure of an X-ray film?

An X-ray film, total thickness approx. 0.5 mm, is made up of seven layers, see figure 1-7:

• a transparent cellulose triacetate or polyester base (d).

On both sides of this base are applied:

• a layer of hardened gelatine (a) to protect the emulsion • emulsion layer (b) which is suspended in gelatine, sensitive to radiation

• a very thin layer called the substratum (c) which bonds the emulsion layer to the base

The normal X-ray film, therefore, has two coatings of emulsion doubling the speed compared to a film with a single emulsion layer. Photographic emulsion is a substance sensitive to ionising radiation and light, and consists of microscopic particles of silver halide crystals suspended in gelatine.

Note: In the past radiography on paper was not unusual. In this ‘ instant cycle’ process results became available within 60 seconds. The quality of the images, however, was extre- mely poor and the life of the film limited to a few months. The availability of better and faster “instant cycle” techniques such as digital radiography (see in a later section), has made radiography on paper obsolete

Schematic corss section of an x-ray film